1. Field of the Invention
The invention relates generally to RF and microwave multiplexers implemented with a plurality of coupled resonators. More specifically, the present invention relates to multiplexers configured to require only a plurality of resonators and series, shunt, cross couplings and input/output couplings between them.
2. Description of the Related Art
Frequency domain demultiplexers and multiplexers are generally used in communication systems to selectively separate (respectively combine) specific signals or frequency bandwidths (these signals or frequency bandwidths also known as channels) from (respectively into) a single signal or frequency band. This objective is usually achieved by the use of coupled resonators bandpass filters (which are usually called channel filters), that freely pass frequencies within specified frequency range, while rejecting frequencies outside the specified limits, and a distribution network that divides (respectively combines) the signals or frequencies going into (respectively coming from) the filters.
Main differences among multiplexers arise from the distribution network, also known as multiplexing network, as filters are always of the coupled resonators type. There are a number of known technical solutions to implement such a network, most commonly used, depending on each particular design, are: multiple-way or cascaded dividers, circulators drop-in chains and manifold networks (i.e. filters connected by lengths of transmission lines: waveguide, coaxial, etc. and “T” junctions).
Description of such multiplexers, and corresponding design theory can be found in the literature: “Design of General Manifold Multiplexers” Rhodes, J. D.; Levy, R.; Microwave Theory and Techniques, IEEE Transactions on, Volume: 27, Issue: 2, February 1979 Pages: 111-123, “A Generalized Multiplexer Theory” Rhodes, J. D.; Levy, R.; Microwave Theory and Techniques, IEEE Transactions on, Volume: 27, Issue: 2, February 1979 Pages: 99-111 and “Innovations in microwave filters and multiplexing networks for communications satellite systems” Kudsia, C.; Cameron, R.; Tang, W.-C.; Microwave Theory and Techniques, IEEE Transactions on, Volume: 40, Issue: 6, June 1992, Pages: 1133-1149.
Usual approach to the design of multiplexers is to separately design each channel filter and then to design the corresponding multiplexing network. In the case of manifold multiplexing, most of the time a final optimization of the elements of the complete multiplexer is needed in order to meet the electrical requirements, and this could be computationally costly when a high number of channels must be optimized using electromagnetic simulations.
FIG. 1 shows a prior art nth order coupled resonator filter used as a building block to implement the above described multiplexers. Each of the boxes represents a resonator (without loss of generality it could be a lumped elements RLC resonator, dielectric resonator, cavity resonator, or any other type of resonator known in the art) and the lines connecting the resonators represent couplings (without loss of generality it could be a lumped element capacitance or inductance, an iris, intercavity apertures, or any other type of coupling known in the art). The filter of FIG. 1 is a canonical one for the nth order, that is, without loss of generality it can implement any nth order transfer function.
FIG. 2 shows a prior art P-channel multiplexer with a 1:P divider multiplexing network.
FIG. 3 shows a prior art P-channel multiplexer with a circulator drop-in chain demultiplexing network.
FIG. 4 shows a prior art P-channel multiplexer with a manifold multiplexing network.
As will be appreciated by those skilled in the art, each of the previously shown configurations present disadvantages: dividers present high insertion losses and/or could have large volume, drop-in chains with circulators are costly and they are not well suited for power applications and finally, manifold networks have large footprints and mass, and they are costly to design and optimize.